Explanation of Database and Data Processing Systems

Database

A database is a self-describing collection of integrated records. It is important that you understand each phrase in this definition, especially because the term database has been given many different meanings. Although database is sometimes used to refer to everything from a collection of index cards to the volumes of data governments collect about their citizens, we will be more precise. A Database Is Self-describing. A database is self-describing in that it contains, in addition to application data, a description of its own structure. This description is called the data dictionary (or the data directory, or metadata, meaning data about data). The data dictionary makes program/data independence possible. In this sense, a database is similar to your college's library. A library is a self-describing collection of books. In addition to books, the library contains a card catalog describing the books in the library. In the same way, the data dictionary (which is part of the database, just as the card catalog is part of the library) contains descriptions of the data contained in the database.

Data Processing Systems

Database technology was developed, in large measure, to overcome the limitations of file processing systems. A new component, the database management system (DBMS), has been added. The DBMS is a program (or a set of programs) that allows stored data to be integrated, reduces data duplication, ensures data integrity, eliminates program dependency on file formats, and allows even complicated objects to be easily represented and retrieved. In short, a DBMS is the program that processes the database. Notice the difference between the file processing system and the database system. File processing programs actually access files of stored data. In contrast, database processing programs call the DBMS to access the stored data. This difference is significant because it makes the application programmer much less concerned with the ways data is physically stored, freeing him or her to concentrate on producing information for the user. In a database system, all application data is stored in a single repository called the database. An application program can ask the DBMS to access customer data, order data, or both. If both are needed, the application programmer needs only to specify how the data is to be combined and the DBMS will perform the necessary operations to combine it. Thus, the programmer is not responsible for the difficult programming needed to coordinate the file processing system. With database processing, duplicate data is minimal. For example, in the record club's database, the member number, name, and address need to be stored only once. Whenever they are needed, the DBMS can retrieve them. And if they are ever modified, only one update will have to be performed. Because data is stored in only one place, data integrity problems seldom occur; there is no opportunity for discrepancies between multiple copies of the same data item. Database processing eliminates the dependency of programs on file formats. All file formats are stored in the database itself (along with the data an interesting and powerful arrangement), and they are accessed by the DBMS, not by application programs.

Application programs need only include a definition (the length and data type) of each of the data items they need from the database. Unlike file processing programs, database processing programs do not require file and record formats. All of those details are handled by the DBMS. This is called program/data independence. With program/data independence, the changes made to the physical format of stored data have a minimal impact on application programs. Those details are used by the DBMS to update its list of physical record and file formats. For the most part, application programs are unaware that any changes have taken place. It also means that whenever data items are added to, changed, or deleted from the database, only the programs that use those particular data items need to be modified. For applications containing dozens of programs, this can represent considerable time savings. Finally, database technology makes it possible to represent, in a straightforward fashion, the objects found in the user's world. An invoice, for example, can be represented by a combination of data extracted from two record types, one record type provides data needed for the fixed-length portion of the invoice, and the second record type supplies data on purchases. There can be a different number of sales records for each member. When an invoice needs to be printed or displayed on a computer screen, the DBMS constructs it by combining the correct data from the two record types.

Imran Zafar writes articles about computer basics and database management such as elements of communication and free computer dictionary.